Mass spectrometer anticipator circuit



Sept 9, 1958 R. L. SINK ET AL MASS SPECTROMETER ANTICIPATOR CIRCUIT 2Sheets-Sheet 1 Filed Sept. 30, 1955 m M w. o m M D W R M. 0 N PL PANELSELECTOR sW/ TCH Dom/SCALE @RWE 65 I II/"ENMTS" ROBET L. 5IN/f PAUL S.GOODWIN BY mi M4z7/ ATTORNEYS Sept 9 1958 R. 1 SINK ET AL4 5h60 MASSSPECTROMETER ANTICIPATOR CIRCUIT Filed sept. 3o, 1955 2 Sheets-Sheet 2bnk .Alfio INVENToRs.

ROBERT l.. s//v/f PAUL s. GOODw//v @Ma-@wm ATTORNEYS United StatesPatent @ffice 2,851,606 Patented Sept. 9, 1958 2,851,606 MASSSPECTROMETER ANTICIPATOR CIRCUIT Robert L. Sink, Altadena, and Paul S.Goodwin, La Canada, Calif., assignors, by mesne assignments, toConsolidated Electrodynamics Corporation, Pasadena, Calif., acorporation of California Application September 30, 1955, Serial No.537,779 Claims. (Cl. Z50-41.9)

This invention relates to a voltage calculator or sensing circuitadapted to direct the operation of an electrically co-ntrolled systemresponsive to the magnitude of voltage signals applied to the sensingcircuit.

This is a continuation-impart application of our copending applicationSerial Number 186,170, led September 22, 1950 now abandoned.

The invention is hereinafter described with relation to its applicationas an anticipator channel for automatic attenuation of a massspectrometer recording system although it will be apparent that such usedoes not in any way represent a limitation on the utility orapplications of the circuit.

The principle of mass spectrometry is in general one of ionizing asample to be analyzed as by an electron beam, segregating ions inaccordance with their massto-charge ratio by inducing spatial separationthereof, and selectively discharging, as at a collector electrode, ionsof a given mass-to-charge ratio. The current developed by discharge of agroup or beam of ions of the same mass-to-charge ratio is proportionalto the partial pressure of the particles in the original sample fromwhich these particular ions are derived. Hence a method is afforded forcalculating the concentration of these particles or molecules in thesample.

in analyzing a sample for more than one component, the segregated ionbeams constituting a part or all of the mass spectrum of the particularsample are successively focussed on the collector electrode so that aplurality of separate discharge currents are obtained, each beingproportional to the number of ions in a particular beam. The massspectrum is scanned in this fashion by varying one or more of theparameters affecting the spatial separation between ions of differingmass-tocharge ratio.

The currents produced by ion discharge are generally converted toappropriate voltages across a dropping resistor, the voltages areamplified, and the amplified signals are recorded on either amultichannel recorder such as an oscillograph or on a single channelrecorder such as a pen and ink recorder. The recorded signals appear asseparate peaks on the record with each peak represent- Ving ions of adifferent givent mass-to-charge ratlo, the recorded trace returning tozero or a base level between succeeding peaks. The peak heights aredetermined by the recorder sensitivity as well as by the nurn-I `ber ofions of the given mass-to-charge ratio represented by the given peak.

Because of the wide differences in the number of 1ons which may beencountered in different beams as a result of wide concentration spreadsin the original sample, 1t is necessary, when using a single c hannelrecorder, to provide means for varying the sensitlvity of the recorderso as to adapt it to this wide variation in ion abundance. lf suchprovision is not made, the less abundant ions of a given spectrum maynot develop a recorded peak .of suicient height on a record having afull scale sensitlvlty such as to accommodate the most abundant ions.This recorder in advance of each separate peak. v

ln U. S. 2,656,498 there is described and illustrated 4a variable rangerecording amplifier suitable for combination with such an anticipatorcircuit. In general, the amplier circuit there shown includes anamplifier and a slidewire potentiometer combined in a null network sothat the balance position of the potentiometer slider is achievedresponsive to the output of the amplifier and gives a measure of themagnitude of the input signal to the amplier. A pen or other recordingmeans is connected to record and excursions of the potentiometer slider.In the patent referred to, variable sensitivity is achieved byconnecting a voltage source'across the potentiometer slidewire andincluding in series therewith means for varying the magnitude of thefull scale voltage across the slidewire. By varying this full scalevoltage, the sensitivity of the network is varied in inverse ratio, itrequiring a greater excursion of the potentiometer slider to arrive at abalanced position as the voltage applied across the potentiometer isreduced, and vice versa. The aforementioned patent suggests attenuationof the variable range recording amplifier by manual selection of theoptimum full scale potentiometer voltage. The anticipator or automaticattenuation circuits of the prior art and of the instant invention areadapted to incorporation with a variable range recording amplifier suchas that described to vary automatically the full scale voltage acrossthe balancing potentiometer in response to the intensity of an ion beamsensed in advance of the time that this beam is focussed on thecollector electrode.

in general, anticipator circuits for this use employ a double collectorsystem in the analyzer tube of the mass spectrometer. The two iontargets are so arranged that a so-called auxiliary or anticipator targetreceives the full ion current signal in advance of the collector target.The anticipator signal is amplified and fed into a calculating devicewhich selects the optimum attenuation range to be used in recording thedata when the same signal later appears at the collector target. Theinformation as to the proper attenuation range is delivered from thecalculator to the main recording channel at a pre-selected timeintermediate the recording of succeeding peaks. Automatic selectorswitches provided in the main channel operate responsive to theinformation derived from the calculator to establish the proper voltageacross the balancing potentiometer.

We have now developed a simplified voltage sensitive calculator which asa mass spectrometer anticipator circuit exhibits greater reliability andgreater flexibility than circuits of like nature described in the priorart. The greater reliability of the circuit of the invention is due inpart to the pro-vision of protective features preventing accidental lossof the information established in the calculator circuit and protectingagainst premature transfer of this information. The voltage sensitiveanticipator circuit of the invention is made repetitive so that aftertransfer of the desired information to the recording channel andattenuation thereof, the calculator will be reset to await the nextsignal.

Accordingly, the present invention contemplates a voltage sensitivecircuit cimprising a stepping relay, a contact meter sensitive to themagnitude of an input voltage to step the relay in accordance therewith,a source of voltage connected through the relay to be delivered therebythrough one of a number of separate channels depending upon the positionto which the relay has been stepped,

and means for resetting the relay after deliverance of the voltagesignal therefrom.

In the particular application above described, the inventioncontemplates in a mass spectrometer having a source of ions, means forsegregating the ions in accord-V ance with their-masstocharge ratio, acollector electrode, means forV successively focussingions of differentmassto-charge ratio on the collector electrode and a variable rangerecording amplifier, the combination comprising an anticipator electrodepositioned in the mass spectrometer to receive ions in advance of thecollector electrode, a stepping relay, means connected between theanticipator electrode and the stepping relay to step the latter inproportion to the current developed at the anticipator electrode, meansoperable responsive to the setting of the stepping relay to vary therange of the recordingv amplifier and as a function of the setting ofthe stepping relay, and means operable to reset the stepping relay afterthe range of the recording amplifier is established thereby.

In its preferred form, the voltage sensing circuit of the inventionincludes elements which prevent premature transfer of the intelligencestored in the stepping relay and likewise prevent premature resetting ofthe stepping relay before the stored intelligence has been utilized.

These and other preferred features of the invention will be more clearlyunderstood by reference to the following detailed description taken inconjunction with the accompanying drawing in which:

Fig. 1 is a schematic diagram of a conventional 180 mass spectrometerprovided with the usual collector electrode and an anticipator electrodefor adapting the mass spectrometer to use with the circuit of theinvention;

Fig. 2 is a circuit diagram of a voltage sensing circuit of theinvention including means for synchronizing its operationl with that ofa mass spectrometer of the type shown in Fig. 1; and

Fig. 3 is a circuit diagram showing one form of interconnecting linkagesuitable for connecting the circuit of Fig.` 2 to a variable rangeamplifier recorder so that information derived in the voltage sensingcircuit may be used to vary the sensitivity range of the massspectrometer recording system.

As might be expected, the application of the voltage sensitive circuitof the invention to the field of mass spectrometry is dependent in partupon modification of the collector system in a conventional massspectrometer. Fig. 1 is a diagram of a modified 180 analyzer type massspectrometer with a collector system adapted for such application. Themass spectrometer comprises an analyzer tube provided at one end with anion source 12. Ions are produced at the-source by an electron beam 13developedat an electron gun 14 and directed across the ion source at anelectron target 15. An accelerating electrode 16 is positionedintermediate the source 12 and an inlet slit 18 in the analyzer tube andby application of suitable potentials between the source andaccelerating electrode and between the accelerating electrode andanalyzer tube, respectively, ions originating at the source arecollimated and propelled as a heterogeneous beam A into the analyzertube. In the analyzer tube, under the influence of a transverse magneticfield established by conventional means (not shown), the heterogeneousion beam A is broken into a plurality of separate beams A1, A2, A3, A4,the ions in each beam being of the same mass-to-charge ratio anddiffering from the mass-tocharge ratio of the ions forming the otherbeams. The number of separate homogeneous beams will, of course, bedependent upon 'the number of components in the sample.

An exit slit 20 in the end of the analyzer tube opposite the ion sourcegives access to an ion collection system.

The collection system includes a collector electrode 22, a metastableion suppressor electrode 23, shield electrodes 24, 2,5 and ananticipator electrode 26. The shield elec- Isignal lagging theanticipator signal.

4 trodes and the metastable ion suppressor electrode are not essentialto the practice of the invention but represent preferred structure.

The anticipator electrode 26 is provided with a slit 26A aligned withand off center with respect to the exit slit 20 in the analyzer tube.Thus ions passing through the exit slit 20 may strike the anticipatortarget 26 or may pass through the slit 26A therein depending upon thefocussing of the beam. In the illustration, the ion beam A1 is out offocus and is discharged at the end wall of the tube. The beam A2 isfocussed through the exit slit and slit 26A in the anticipator target tostrike the collector electrode 22 while the beam A3 likewise is focussedthrough the exit slit 2,0 but onto the anticipator target and the beamA4 has not yet been brought into focus on the exit slit and strikes'andl discharges on the walls of the analyzer tube. In scanning andspectrum, the ion beams are shifted to the left with respect to the exitslit so that beam A2 will shift out of focus with respect to the exitslit 20, beam A3 will focus through the slit 26A of the anticipatortarget and beam A4 will be brought into focusthrough the exit slit 20and onto the anticipator target.

The exit slit 20 is made just wide enough to receive adjacent masses,while the'slit 26A in the anticipator target is narrow enough to resolvebetween adjacent masses, these relationships being maintained for thehighest mass range to be encountered in any given instrument. Thus it isconventional to design a mass spectrometer to analyze materials within agiven mass range and in the present instance the exit slit and slit inthe anticipator target are proportioned as described and with-respect tothe highest ion masses to be encountered. Spatial separation betweenadjacent ion masses is a function of the reciprocal of the ion masses sothat resolution of high mass ions automatically insures resolution oflower mass ions.

It is apparent from the foregoing descriptionof the collection system ofthe mass spectrometer that the ion discharge signals developed at eachof the anticipator and collection targets are the same with thecollector This means that by the time the collecting channel recorderhas started to record a peak responsive to the discharge of ions of agiven mass at the collector electrode, the crest of that same peak must,of necessity, have passed and previously discharged on the anticipatortarget. This characteristic of the system insures that the top of thepeak has reached the anticipator target and that no further signalincreases will occur in the anticipator channel until the next peakarrives.

As mentioned above, another characteristic of the collector system,which is important to the use of the circuit of the invention as ananticipator channel, is that all peaks return substantially to zero orto a base level before the arrival of the next peak. This is insured byproper dirnensioning of theA slit system so that slit 26A will resolveadjacent masses up to the largest mass to be encountered, and exit slit20 in the analyzer tube will resolve between alternate adjacent massesso that only one mass at a time will strike the anticipator electrode.

Fig. 2 is a diagram of the voltage sensitive circuit of the invention asadapted for use in conjunction with the mass spectrometer shown in Fig.l. The circuit includes an amplifier 30 with the anticipator target 26connected to the amplifier input through. a dropping resistor 32 to feeda voltage to the amplifier which is proportional to the ion dischargecurrent developed at the anticipator target. The circuit also includes afirst contact meter 34 and a second contact meter 35 connected toreceive the output of the amplifier 30. The contact meters areessentially identical including, respectively, indicating pointers 34A,35A, hand set pointers 34B, 35B, indicating coils 34C, 35C and lockingcoils 34D, 35D. A stepping relay 38 is connected to be actuatedresponsive to the condition of the contact meters and includes aplurality of output channels identied as x1, x3, xll, etc., a pluralityof input channels similarly identiiied and a companion pair of movablecontacts 38A, 38B which respectively contact corresponding input andoutput channels upon movement thereof. The stepping relay 38 is providedwith a stepping coil 38D for stepping the contacts 38A, 33B upscale anda resetting coil 38C, the function of which is described in greaterdetail hereinafter. The hand set arm 34B of contact meter 34 isconnecfed through the coil of a relay 40 to a relay 42, the latter ofwhich operates as an interrupter to continuously make and break thecircuit between the indicating arm 34A and contact arm 34B when thecurrent supplied to the indicating arm 34A is sufficient to carry itinto contact with the hand set arm 34B.

A pen-operated micro-switch 44 is connected to govern the application ofan output signal from the stepping relay and the resetting of thestepping relay in the proper sequence and at the proper time withrelation to the condition of the main recording channel. The switch 44includes a cam 44A driven in opposite directions responsive to upscaleand downscale movement of the recording pen on a variable-rangeamplifier and recorder 45 (see Fig. 3), say of the type disclosed in U.S. 2,656,498, micro-switches 44B, 44C and a lever 44D, which is normallyurged toward a neutral position between micro-switches 44B and 44C by aspring 44E. The recording pen is coupled to rotate the cam 44A throughmechanical link 44F (see Fig. 3). The cam is arranged so that themicro-switch 44C closes as the recording pen approaches the base line orzero, i. e. at the tail end of a peak. As explained below, this causesthe recording arnplier to change to the sensitivity selected by relay38. The micro-switch 44B closes to reset the relay 38 as the recordingpen leaves the base line to record a peak. As explained below, thisoccurs after micro-switch44C has closed and reopened, and the operationof the microswitch 44B to reset relay 38 does not disturb the recordingampliiier. The lever is operable responsive to movement of cam 44A toactuate switch 44C as the recording pen moves downscale, and to actuateswitch 44B as the recording pen moves upscale. The switch 44C isconnectcd in series between voltage source 46 and contact 38B of relay38 and switch 44B is connected in series between the voltage source andreset coil 38C of relay 38.

The hand set arm 35B of the second contact meter is connected throughthe coil of a relay 48, which in turn is connected in series withcontacts 48B to the negative side of the source 46. When arm 35Bcontacts arm 35A, it is connected through coil 35D and contacts 48C toground and to the positive side of the potential source 46. When thearms thus make contact, while contacts 48B are closed, the coil 48 isenergized as also is the locking coil 35D.

The operation of the circuit of Fig. 2 can be better understood after abrief description of Fig. 3 which shows means for using the informationobtained from the circuit of Fig. 2 to Vary the range of a Variablerange recording amplifier. Briefly, the stepping relay 3S in Fig. 2steps to one of the several output channels x1, x3, x10, etc., dependentupon the magnitude of the voltage introduced to the amplifier 30. Thedesignations x1, x3, etc., as applied to various contact points andconnecting leads in the circuits of Figs. 2 and 3 signify thatcorrespondingly identified elements are component parts of separatechannels which are appropriately selected in a manner hereinafterexplained to control the magnitude of the full scale voltage across thebalancing potentiometer found in a recording amplifier of the typepreviously described. Thus the channel represented by the severalelements labeled x3 is connected, when energized, to increaseautomatically the voltage across such a balancing potentiometer by afactor of 3. The sensitivity of the recording amplifier circuit will, asa result, be altered by the recip- 6 rocal of this factor. The means ofaltering this sensitivity responsive to the setting of the steppingrelay 38 is shown diagrammatically in Fig. 3.

Referring to this figure, the automatic attenuation system includes apanel selector switch 60 by means of which attenuation may be selectedmanually, and also includes a contact labeled auto auto. which connectsthe circuit for automatic selection. The stepping relay 38 as shown inFig. 3 constitutes only that portion of the relay comprising the outputchannels. The variable range ampliier and recorder 45 includes apotentiometer (not shown), the movable tap of which is mechanicallyconnected to a bi-directional stepping relay 60 including ganged contactwafers 62, 63 an upscale drive coil 64 and a downscale drive coil 65.

A source of voltage, say the source 46 of Fig. 2, is connected throughthe panel selector switch when in the auto. position illustrated and thestepping relay to one of the common buses designated x1, x3, x10, etc.,interconnecting the contact points of the relay wafers 62, 63. Thewafers 62, 63 are arranged so that they will home to the maximumposition attained by the stepping relay 38 for each distinct dischargesignal received at the anticipator target.

The two wafers 62 and 63 are composed of conductive material and areganged together by linkage 66 so that they rotate in the same direction.The wafers 62 and 63 are driven respectively by solenoids 64 and 65through mechanical links 70. When the solenoid 64 is energized, itcauses the wafers to rotate in a clockwise direction. When the solenoid65 is energized, it causes the wafers to rotate in a counter-clockwisedirection. Another mechanical linkage 66A is interconnected with thevariable range amplier and recorder 4S, providing a mechanical couplingbetween the homing switch and the variable range amplifier and recorderso that the voltage across the balancing potentiometer can be varied inrespouse to movement of the homing switches. Each of thc solenoids isconnected in series with a normally closed breaker contact 69. Cams 67on the shafts which support the wafers actuate these contacts throughmechanical linkages 65. By the cams action of breaking the solenoidscurrent, the solenoid is energized in a stepwise manner, and the waferis caused to rotate. For each step the rotation of the wafer is equal tothe angular spacing between the brushes which contact the outerperiphery of the wafer, and the cams are spaced on the shafts so as tointerrupt the contacts with such frequency that the movement with eachstep is equal to that angular distance, as between contacts x1 and x3.

The operation of the circuit of Fig. 3 will be best understood after adetailed description of the operation of the circuit of Fig. 2 whichfollows:

The D. C. amplifier 3() has as its input the signal developed at theanticipator target 26 across the dropping resistor 32. The output of theamplifier is a voltage whose amplitude is directly proportional to theinput current. As the ion current to the anticipator target increasesduring the scan of a mass peak, the ampliiier output voltage increasesin a negative direction. At a predetermined level of output voltage, saya level corresponding to approximately 15% of full scale on the mostsensitive range of the main recorder 45, indicating pointer 34A ofcontact meter 34 contacts the hand set contact pointer as a result ofcurrent flow through indicating coil 34C. When contact is establishedbetween the indicating and hand set pointers, current will flow throughcoil 34D and its associated circuit. The two pointers are thusmagnetically locked together so that the indicating pointer isindependent of signal current in the indicating coil. The coil of relay40 is connected across a capacitor 40A in series with the locking coil34D. The relay 40 is a necessary element of the circuit because themeter contacts can not carry sutiicient current to operate reset coil38C of relay 38. The contacts of relay 40am connected between the resetcoil 38C of the relay 38 andgroundandare arrangedv to open-circuit thereset coil when relay 40 is energized byestablishment of contact inmeter 34. The relay l40 therefore prevents reset of relay 38u/,hen thereis asignificant signal at theauxiliary target.

Relay 42.is. connectedrin series with both the relay 40 and the lockingcoil 341Dl of contact meter34. The relay 42. is vurged by atension-;spring 42Ato complete the circuit throughthe c oil of relay 42so that it operates as a lowv frequency interrupteror buzzer, andperiodically open-circuits the locking coil. for short intervals. Duringsuch interruptions, theresulting collapsing field in the locking coilwill kick the indicator pointer away from the contact pointer. As longasthe signal applied to the indicating coil d34C from the amplifier isabove the level set on the hand set vvpoin terthe indicating pointerwill returnimrnediately to re-establish contact with the hand setpointer. The condenser 40A connected across the coil of relay 40 is madelarge enough so that the short interruptionscaused by the alternation ofrelay 42 will not actuate the contacts of the relay 40. For this reasonthe reset mechanism is rendered inoperative whenever the ion signal atthe auxiliary target is at a value representingrnoretl'lan 15% of fullscale on the most sensitive recordingl range. However, when this ionsignal falls below full scale, the indicating pointer is not broughtback intocontact with the hand set pointer after interruption by relay42 `and the relay 40 is de-energized. At this point one conditionnecessary to actuation of the reset mechanism of relay 38 will obtain.

lThe automatic attenuation jfunction of the circuit is accomplishedbythe, secondcontact meter 35 and the associated stepping relay 38.Starting in lthe most sensitive region(x1 scale) an increasingsignalwill cause the indicating pointer 35A of this meter to swingupscale because of current flow through the indicating coil 35C. Whenthe indicating pointer reaches approximately 95% of full scale, contactis made with the. hand set pointer and they are locked togetherbyrcurrent ow through the locking coil 35D in a manner similar to thatdescribed with reference to contact meter 34. Relay 48, associated withcontact meter 35is a combination control and interrupting relay.Contacts 48B, 48C of relay 48 are urged by tension spring 48D to theposition shown in Fig. 2. When the indicating and hand set pointers ofthe meter 35 make contact, current tiows through both the coil of relay48 and the' locking coil35D of the meter. The time constant of the coiland relay 48 and of an associated condenser 48A connected across thecoil is adjusted to give a small delay to the operation of the relaycontacts to insure good Contact of the meter pointers. When the contactsof relay 48 to the energized position, one set 48C interrupts thelocking current in the meter to give the indicatingpointer a kick downscale by reason of the decay of the field in the locking coil and at thesame time energizes the stepping coil 38D of the stepping relay. Thestepping relay is thus advanced from the assumed x1 position to the x3position, thev contacts 38A, 38B moving simultaneously to the twopositions. The other set of contacts 48B on the relay 48 opens thecircuit on the other side of the locking coil 35D to eliminate anycurrent flow from the voltage source 46 through the indicating coil 35Cin the reverse direction.

The aforementioned time constant of the relay 48 serves the additionalfunction of keeping the relay in the energized position long enough forthe stepping relay 38 to be driven one step forward even though thelocking current in the contact meter 35 has been interrupted. During thetime the stepping relay is being actuated, the indicating pointer 35A ofthe meter 35 is being pulled back towards zero bythe internal springaction of the meter because the signal current has been removed from theindicating coil by contacts 48C. As soon as the relay 48 returns to itsde-energized position, the signal current will again position. theindicating pointer 35A according to the signal magnitude, and the drivemechanism of the stepping relay will return to its quiescentpposition toawait the next step. If the ion signal current as amplified in theamplifier 30 is large. enough to drive the indicating pointer 35A to 95of full scale on the x3 range, the above processrepeats to drive thestepping relay to the x10 position. It should be noted that with eachstep of contact 38A of the stepping relay, the sensitivity of thecontact meter 35 is reduced by reason of the resistance added to thecircuit between the amplifier and the contact 38A. The stepping processcontinues until an on scale reading is achieved on the contact meter 35.This reading will lie between 3.0% and of full scale on the meterregardless of the range, with the possible exception of the x1 rangeWhen the initial signal may be less than 30% of full scale.

As the maximum value of the ion discharge signal is passed, and thesignal decreases in magnitude, the indicating pointer 35A will followthe signal back to zero following interruption of the locking coilcircuit. However, at this condition the position of the stepping relaywill remain unchanged as there is no means by which it can be stepped inthe reverse direction. Thus the stepping relay remains at its maximumvalue even though the signal drops below 15% of full scale on the x1range and the contact meter 34 will allow reset by reason of thede-energization of relay 40. A second preventative feature is provided.by the pen operated switch 44. The micro-switch 44B is in series withthe reset coil 38C of relay 38 and is kept open until the range selectedby the relay is transferred from the contacts x1, x3, x10, etc. to thehoming switch in Fig. 3 through micro-switch 44C. Once the mainrecording amplifier is set to the new attenuation range, themicro-switch 44B closes due to the upscale movement of the pen andcompletes the circuit through theV reset coil 38C, whereupon thestepping relay is returned to the x1 position to await the incidence ofthe next succeeding peak on the anticipator target.

The micro-switch 44C opens due topen upscale movement prior to theclosure of the micro-switch 44B. For this reason resetting of thestepping relay 38 to the x1 position does not disturb the setting of thewafers 62 and 63, and hence the attenuation range of the amplifier 60 isnot affected by the resetting operation. This control action of themicro-switch 44C will be apparent from an inspection of Fig. 3 of thedrawings.

Thus, the stepping switch 38 is actuated during each period when an ionbeam impinges upon the anticipator target 26, and the information as tothe desired recording level is transferred to the homing switches 62, 63when the recording pen of the pass spectrometer approaches its base lineso that the pen operated microswitch 44 causes the contacts 44C toclose. The position of the homing switches 62, 63 and hence theattenuation range of the amplifier 60, is not changed again until therecording pen records the next peak and again approaches its base lines.In this manner, the homing switches 62, 63 store the information as toeach desired recording level until the respective ion beams traverse thecollector electrode 22 of the mass spectrometer.

The stepping switch 38 is reset when the recording pen of the massspectrometer begins to record a peak because at that time the penoperated micro-switch 44 first causes the contacts 44C to open and thenthe contacts 44B to close. Since the setting of the switch 38 is nottransferred to the homing switches 62, 63 until the recording pen of themass spectrometer completes the recording of the peak, the recordinglevel is not changed until after the peak is recorded.

As described above, cam 44A and lever 44D are so arranged thatmicro-switch 44C is closed as the recording pen approaches zero afterrecording a peak. By this time relay 38 has been set at the properattenuation level for the succeeding peak and this information istransferred to the recorder when micro-switch 44C is closed. As therecording pen moves upscale to record the new peak, micro-switch 44C isopened and micro-switch 44B is closed. This completes the circuitthrough reset coil 38C of relay 38 and allows the relay to be resetwhenever relay 40 is de-energized.

Referring now to Fig. 3, the setting of the stepping relay 38 on any ofthe x1, x3, x10, etc., positions closes the circuit through micro-switch44C between the voltage source 46 and one of the homing switches 62, 63so that the latter homes to a position corresponding to the setting ofthe stepping relay. In so doing the homing Switch operates to vary thefull scale voltage across the balancing potentiometer of the variablerange amplier 45. In the x1 position shown in Fig. 3 there is no currentflow through either of the homing switches 62, 63, and hence there is noflow through their respective associated actuating coils 64, 65. Now ifthe stepping relay moves to the x3 position for a different ion peak acircuit is completed through the x3 bus to homing switch 62 and theactuating coil 64, the latter being thereupon energized to rotate switch62 and the yganged switch 63 clockwise until the circuit through theswitch 62 is broken. If the stepping relay then steps to the x positionfor a third peak a circuit is completed through bus x10 and the switch62 to again actuate the driving coil 64 to rotate the switches one step.In this procedure the contact wafer of switch 63 will rotate clockwiseto the position where it makes contact with xl, x3 contact. If on thenext peak the stepping relay reaches the x3 position only, the homingswitch drive will be through the downscale drive switch 63 and itsdriving coil 65 to reverse the direction of rotation of the homingswitches as that attenuation of the amplier will be at the x3 instead ofthe x10 level.

This process is kept up through the entire mass spectrum so that themain recording amplifier will scan each peak in turn at the properattenuation setting. The time constants, etc., are established for thecritically adjacent mass peaks which are the largestmasses likely to beencountered in the particular instrument. The entire circuit is madefast enough to respond to these masses without impairing its performanceat the opposite end of the mass range where the peaks are much fartherapart in time.

Referring again to Fig. l, the exit slit of the mass spectrometer shouldbe just wide enough to receive the two most closely spaced ion beamswhich the apparatus is designed to record. Since the exit slit Ztl andthe slit 26A in the anticipator target 26 are offset, only one ion beamis allowed to impinge upon the anticipator electrode at a time. Withsuch an arrangement the recording level of the apparatus is set inaccordance with the intensity of only one ion beam at a time.

To facilitate interpretation of the resultant record it is convenient toinclude some type of coding means to identify on the record injuxtaposition to each peak the attenuation range at which that peak wasrecorded. One such recording circuit is described in U. S. 2,656,498,

The pen operated micro-switches 44B, 44C act as an interlock to preventpremature transfer of information from the anticipator to the recordingchannel and also to prevent resetting of the anticipator channel beforethe information is transferred. Other interlock means may be employed asfor example the arrangement described in U. S. 2,629,056.

We claim:

1. A voltage sensitive circuit comprising a stepping relay having astepping winding and a resetting winding, a contact meter connected tothe stepping winding of the relay and sensitive to the magnitude of aninput voltage to step the relay in accordance therewith, a source ofvoltage connected to the relay to be delivered thereby through one of anumber of separate channels selected by the relay, and a second contactmeter connected to 10 the resetting winding of the relay for resettingthe relay responsive to decay of said input Voltage.

2. A voltage sensitive circuit comprising a stepping relay, a contactmeter sensitive to the magnitude of an input voltage to step the relayin accordance therewith, means for decreasing the sensitivity of saidcontact meter for each upscale step of the stepping relay, a source ofvoltage connected to the relay to be delivered thereby through one of anumber of separate channels selected by the relay, and means forresetting the relay responsive to decay of said input voltage.

3. A voltage sensitive circuit comprising a stepping relay, a firstcontact meter sensitive to the magnitude of an input voltage to step therelay in accordance therewith, means for decreasing the sensitivity ofsaid contact meter for each upscale step of the stepping relay, a sourceof voltage connected to the relay to be delivered thereby through one ofa number of separate channels selected by the relay, and a secondcontact meter operable to reset the stepping relay responsive to decayof said input voltage below a predetermined Value.

4. A voltage sensitive circuit comprising a multichannel stepping relayincluding a stepping coil and a reset coil, a voltage source connectedto the stepping relay for delivering a voltage signal through one ofsaid channels as determined by the setting of the stepping relay, afirst contact meter adapted to receive a current proportional to thevoltage input to said circuit and to make contact when the voltage inputreaches a predetermined value, means preventing energization of saidreset coil when Contact is established in said first contact meter, asecond contact meter adapted to receive a current proportional to thevoltage input to the circuit, means for varying the proportionalitybetween the current to the second Contact meter and the input voltagefor each step of the stepping relay, and means operable to energize saidstepping coil when contact is established at said second contact meter.

5. A voltage sensitive circuit comprising a multichannel stepping relayincluding a stepping coil and a reset coil, a voltage source connectedto the stepping relay for delivering a voltage signal through one ofsaid channels as determined by the setting of the stepping relay, a rstcontact meter adapted to receive a current proportional to the voltageinput to said circuit and to make contact when the voltage input reachesa predetermined value, means preventing energization of said reset coilwhen contact is established in said first contact meter, an interrupterrelay adapted to intermittently break the circuit through said lirstcontact meter, a second contact meter adapted to receive a currentproportional to the voltage input to the circuit, means for varying theproportionality between the current to the second contact meter and theinput voltage for each step of the stepping relay, and means operable toenergize said stepping coil when contact is established at said secondcontact meter.

6. A voltage sensitive circuit comprising a multichannel stepping relayincluding a stepping coil and a reset coil, a voltage source connectedto the stepping relay for delivering a voltage signal through one ofsaid channels as determined by the setting of the stepping relay, a rstcontact meter adapted to receive a current proportional to the voltageinput to said circuit and to make contact when the voltage input reachesa predetermined value, means preventing energization of said reset coilwhen Contact is established in said first contact meter, an interrupterrelay adapted to intermittently break the circuit through said iirstcontact meter, a second contact meter adapted to receive a currentproportional to the voltage input to the circuit, means associated withthe stepping relay to vary the proportionality between the current tothe second contact meter and the input voltage for each stepof thestepping relay, and means operable 11 to venergize said stepping coilwhen contact is established at said second contact meter.

7. Apparatus according to claim 6 wherein the means for varying theproportionality between the' current to said second meter and the inputvoltage comprises a bank of resistors connected in series with the inputvoltage, an adjustable slider connected to the input of said secondmeter, and means causing said slider to tap oi an additional resistorfor each upscale step of said stepping relay.

8. In a mass spectrometer having a source of ions, means for segregatingthe ions in accordance with their mass-to-charge ratio, a collectorelectrode, means for successively focusing ions of differingmassto-charge ratio on the collector electrode, a variable rangeamplifier and recorder, an automatic sensitivity selection circuitcomprising an anticipator electrode positioned to receive ions inadvance of the collector electrode, an amplifier connected to amplifydischarge signals developed at the anticipator electrode, a steppingrelay, a contact meter sensitive to the magnitude of the output of saidamplifier to actuate and step the stepping relay in accordance with themagnitude of the amplifier output, means for decreasing the sensitivityof the meter for each upscale step of the relay, a source of voltageconnected to the relay, and means kfor varying the adjustment of thevariable range amplifier and recorder in accordance with the setting ofsaid `stepping relay.

9. In a mass spectrometer having a source of ions, means for segregatingthe ions in accordance with their mass-to-charge ratio, a collectorelectrode, means for successively focusing ions of diieringmass-to-charge ratio on the collector electrode, a variable rangeamplifier and recorder, an automatic sensitivity selection circuitcomprising an anticipator electrode positioned to receive ions inadvance of the collector electrode, an amplifier connected to amplifydischarge signals developed at the anticipator electrode, a steppingrelay, a contact meter sensitive to the magnitude of the output of saidamplifier to actuate and step the stepping relay in accordance with themagnitude of the amplier output, means for decreasing the sensitivity ofthe meter for each upscale step of the relay, a source of Voltageconnected to the relay, means vfor varying the adjustment of thevariable range amplifier and recorder in accordance with the .setting ofsaid stepping relay, means for resetting said stepping relay, andcontrol means for timing the variation of the variable range amplifierand recorder adjustment and resetting of said stepping relay inaccordance with the condition of said recorder.

10. Apparatus according to claim 9 wherein said control means comprisesa pair of micro-switches, a first one of said switches being connectedin series with said means for resetting said stepping relay, and thesecond of said switches being connected in series with said means forvarying the adjustment of variable range amplifier and recorder, andmeans operable responsive to movement of the 'recorder to close saidsecond switch and to open said rst switch as the recorder approacheszero and to reverse the switch positions as the recorder leaves zero.

References Cited in the file of this patent UNITED STATES PATENTS2,575,711 .Hippie et al. Nov. 20, 1951 2,650,306 Robinson Aug. 25, 19532,661,260 Salzman Dec. 1, 1953

